Expandable and adjustable lordosis interbody fusion system

ABSTRACT

An expandable housing for an interbody fusion system has movable tapered external helical threaded members that travel along tracking to operably engage against the top and bottom shell members, urging them apart to cause expansion in the height of the housing. In an embodiment, the tapered members are disposed in a dual arrangement such that independent engagement of the tapered members along lateral portions of the top and bottom shells cause an angular tilt to the exterior surface of the housing when the tapered members are moved to different degrees. This function permits adjustment in the angular relationship between adjacent vertebrae and assists the lordotic adjustment of the patient&#39;s spine. When the functions of the device are used in combination by the surgeon, the device provides an effective tool for in situ adjustment when performing lateral lumbar interbody fusion.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/859,241 filed Dec. 29, 2017 entitled “EXPANDABLE AND ADJUSTABLELORDOSIS INTERBODY FUSION SYSTEM,” which is a continuation of U.S.application Ser. No. 14/473,200 filed Aug. 29, 2014 entitled “EXPANDABLEAND ADJUSTABLE LORDOSIS INTERBODY FUSION SYSTEM,” which claims priorityto U.S. provisional patent application No. 61/871,780 filed Aug. 29,2013 entitled EXPANDABLE LATERAL INTERBODY FUSION SYSTEM, thedisclosures of all of which are hereby incorporated by reference intheir entirety.

TECHNICAL FIELD

The invention relates to surgical procedures and apparatus for treatinglumbar back pain.

BACKGROUND

Lumbar spinal fusion is a surgical procedure to correct problemsrelating to the human spine. It generally involves removing damaged discand bone from between two vertebrae and inserting bone graft materialthat promotes bone growth. As the bone grows, the two vertebrae join, orfuse, together. Fusing the bones together can help make that particulararea of the back more stable and help reduce problems related to nerveirritation at the site of the fusion. Fusions can be done at one or moresegments of the spine.

Interbody fusion is a common procedure to remove the nucleus pulposusand/or the annulus fibrosus that compose the intervertebral disc at thepoint of the back problem and replace it with a cage configured in shapeand dimension to restore the distance between adjacent vertebrae to thatof a proper condition. Surgical approaches to implement interbody fusionvary, and access to the patient's vertebral column can be made throughthe abdomen or back. One other surgical method for accomplishing lumbarspinal fusion in a less invasive way involves accessing the vertebralcolumn through a small incision on the side of the body. This procedureis known as lateral lumbar interbody fusion.

Once the intervertebral disc is removed from the body during the laterallumbar interbody fusion, the surgeon typically forces different trialimplants between the vertebral endplates of the specific region todetermine the appropriate size of the implant for maintaining a distancebetween the adjacent vertebrae. Another consideration is to maintain thenatural angle between lumbar vertebral bodies to accommodate thelordosis, or natural curvature, of the spine. Therefore, duringselection of a cage for implantation, both intervertebral disc heightand lordosis must be considered. Prior art fusion cages are oftenpre-configured to have top and bottom surfaces angles to one another toaccommodate the natural curvature of the spine. It is unlikely thatthese values can be determined precisely prior to the operation, whichis a drawback in present procedures. Prepared bone graft is generallypacked into the cage implant once it is properly sized and before it isinserted in between the vertebral bodies.

Present lateral interbody fusion cage devices are generally limited toproviding height expansion functions, but not a lordotic adjustmentcapability. In implementing a trial-and-error approach to sizing andfitting the interbody fusion cage into the target region for theparticular geometric configuration for that patient, the patient issubjected to significant invasive activity. The bone graft material isgenerally added and packed in to the fusion device after the desiredheight expansion has been reached and final adjustments made.

SUMMARY

An embodiment of the device comprises an expandable housing comprised ofopposing shell members. Movable tapered screw-like elements having anexternal helical thread are disposed in the housing and operably engageagainst the top and bottom shell members, urging them apart to causeexpansion in the height of the housing. This function permits adjustmentof the distance (height) between adjacent vertebrae when in place. Thetapered members are disposed in a dual arrangement such that independentengagement of the tapered members along lateral portions of the top andbottom shells cause an angular tilt to the exterior surface of thehousing when the wedge members are moved to different degrees. Thisfunction permits adjustment in the angular relationship between adjacentvertebrae and assists the lordotic adjustment of the patient's spine.When the functions of the device are used in combination by the surgeon,the device provides an effective tool for in situ adjustment whenperforming lateral lumbar interbody fusion.

An embodiment of the device further comprises a track configurationwithin the housing for guiding the tapered external helical threadedmembers in their engagement with the top and bottom shell members. Thetrack comprises raised elements on each of the interior surfaces of thetop and bottom shell members that permit an interlocking engagement forlateral stability of the housing when in a contracted position. As thehousing expands, the track area provides space for storage of bone graftmaterial. One embodiment may provide for an elastic membrane to bepositioned around the housing to prevent bone graft material fromseeping out of the cage and to provide a compressive force around thecage to provide structural stability to the housing.

An embodiment of the device further comprises drive shafts for operatingthe tapered external helical threaded members. The drive shafts permitthe surgeon, through the use of a supplemental tool, to manipulate theshafts which operatively move the tapered external helical threadedmembers in controlling the expansion of the housing and angularadjustment of the top and bottom shell members for in situ fitting ofthe interbody fusion device. A locking mechanism is provided forpreventing rotation of the shafts when the tool is not engaged and aftermanipulation by the tool is completed. The tool also facilitatesinsertion of bone graft material into the fusion body during in situadjustment.

An embodiment of the present invention provides a surgeon with theability to both expand the fusion cage and adjust the lordotic angle ofthe fusion cage in situ during operation on a patient and to introducebone graft material at the operation site while the device is in place.This embodiment of the present invention therefore provides a fusioncage having geometric variability to accommodate the spinal conditionunique to each patient.

Embodiments of the present invention therefore provide an interbody cagedevice for use in lateral lumbar interbody fusion procedures thatcombines the functions of height expansion for adjusting the distancebetween adjacent vertebrae with lordotic adjustment to control theangular relationship between the vertebrae. Embodiments of the inventiveinterbody cage device further provide a storage capacity for containingbone graft material in the interbody cage device as disc height andlordotic adjustment takes place in situ.

The present invention also provides a device that may be used inenvironments other than in interbody fusion applications. It maygenerally be used to impart a separating effect between adjacentelements and to impart a variable angular relationship between theelements to which it is applied.

These and other features of the present invention are described ingreater detail below in the section titled DETAILED DESCRIPTION OF THEINVENTION.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention is described herein withreference to the following drawing figures, with greater emphasis beingplaced on clarity rather than scale:

FIG. 1 is a view in side elevation from the side of the expandable shelldevice.

FIG. 2 is a perspective view of a bottom section of the expandableshell.

FIG. 3 is a top plan view of the bottom section of the expandable shell.

FIG. 4 is a top plan view of the expandable shell device.

FIG. 5 is a perspective view of a tapered external helical threadedmember.

FIG. 5A is a view in side elevation from the side of the taperedexternal helical threaded member.

FIG. 5B is a view in side elevation from the front of the taperedexternal helical threaded member.

FIG. 6 is a cross-sectional view of the device taken along lines 6-6 inFIG. 1.

FIGS. 7A-7C are a series of views in side elevation of the device as itundergoes expansion.

FIG. 8 is a view in side elevation of the device showing an expansion ofthe device to accommodate a lordotic effect.

FIG. 9A is a perspective expanded view of thrust bearing for the driveshaft.

FIG. 9B is a perspective view of the drive shafts and thrust bearings.

FIG. 9C is a top plan view in cross section of the area of engagement ofthe drive shafts with the thrust bearings.

FIG. 10 is a side elevation view of the housing as expanded.

FIG. 11A is a top plan view of another embodiment of the device.

FIG. 11B is a top plan view of yet another embodiment of the device.

FIG. 12A is a top plan view of the drive shafts disengaged by thelocking mechanism.

FIG. 12B is a top plan view of the drive shafts engaged by the lockingmechanism.

FIG. 13A is a perspective view of the locking mechanism.

FIG. 13B is a top plan cross sectional view of the drive shaftsdisengaged by the locking mechanism.

FIG. 13C is a top plan cross sectional view of the drive shafts engagedby the locking mechanism.

FIG. 14 is a view taken along lines 14-14 in FIG. 11A.

FIGS. 15A-C are a series of views in side elevation taken from the endof the device as it undergoes expansion showing the lordotic effect.

FIG. 16 is a perspective view of the operating tool.

FIG. 17 is a view showing a manner of attachment of the operating toolto the drive shafts of the device.

FIG. 18 is a breakaway perspective view of the handle of the operatingtool.

FIG. 19 is a perspective view of gears in the handle engaged foroperation of both drive shafts.

FIG. 20 is a perspective view of gears in the handle disengaged foroperation of a single drive shaft.

DETAILED DESCRIPTION OF EMBODIMENTS

With reference to the drawings figures, an interbody fusion body deviceis herein described, shown, and otherwise disclosed in accordance withvarious embodiments, including preferred embodiments, of the presentinvention. The interbody fusion device 10 is shown generally in FIG. 1.It is comprised of a housing 12 having a top shell 14 and a bottom shell16. The overall housing may have a length of 50 mm and a width of 20 mm,as an example. The shell material may be comprised of a suitablematerial, such as titanium alloy (Ti-6AL-4V), cobalt chromium, orpolyether ether ketone (PEEK). Other materials may be suitable that canprovide sufficient compositional integrity and that have suitablebiocompatible qualities. The interior of the shells are configured witha cascading step tracking 18 and 20 placed along their lateral edges. Asshown in FIG. 2, step tracking 18 begins towards the midpoint of aninner surface of bottom shell 16 with successive track steps increasingin height as the tracking extends to a first end of bottom shell 16.Correspondingly, step-tracking 20 begins towards the midpoint of theinner surface of bottom shell 16 with successive track steps increasingin height as that portion of the tracking extends to a second oppositeend of bottom shell 16. Step tracking 18 comprises dual track runs 22and 24 while step tracking 20 comprises dual track runs 26 and 28 asshown in FIG. 3. Corresponding step tracking 30 and 32 is provided ontop shell 14 as shown in FIG. 4. When the device is in its fullycompressed state where top shell 14 lies adjacent to bottom shell 16, asshown in FIG. 1, step tracking 18 intermeshes with step tracking 30 andstep tracking 20 intermeshes with step tracking 32.

The respective track runs comprise a series of risers, or track steps,which are spaced apart to receive the threads of tapered externalhelical threaded members. The tapered external helical threaded membersprovide a wedging action for separating the top and bottom shell therebyincreasing the height of the housing to effect expansion between thevertebral bodies in which the device is placed. As shown in FIG. 4,track run 22 receives tapered external helical threaded member 34, trackrun 24 receives tapered external helical threaded member 36, track run26 receives tapered external helical threaded member 38, and track run28 receives tapered external helical threaded member 40. Track run 22aligns collinearly with track run 26 such that the travel of taperedexternal helical threaded members 34 and 38 within the respective trackruns occurs within that collinear alignment. The thread orientation oftapered external helical threaded members 34 and 38 are opposite of eachother such that their rotation will result in opposite directionalmovement with respect to each other. As shown in FIG. 4, a drive shaft42 runs along the collinear span of track runs 22 and 26 and passesthrough tapered external helical threaded members 34 and 38. Shaft 42has a square cross sectional configuration for engaging and turning thetapered external helical threaded members. As shown in FIG. 5, thecentral axial opening 44 of the tapered external helical threadedmembers are configured to receive and engage the shaft 42. Shaft 42 mayalternatively comprise any shape for effectively creating a spline, suchas a hexagonal shape, and central axial openings 44 may comprise acorresponding configuration for receiving that shape. As shaft 42 isrotated by its end 48 in a clockwise direction, tapered external helicalthreaded members 34 and 38 are rotated and their respective threadorientations cause the screws to travel apart from each other alongtrack run 22 and track run 26, respectively. Correspondingly, as shaft42 is rotated by its end 48 in a counter-clockwise direction, taperedexternal helical threaded members 34 and 38 are caused to travel towardseach other along track run 22 and track run 26, respectively.

Similarly, track run 24 aligns collinearly with track run 28 such thatthe travel of tapered external helical threaded members 36 and 40 withinthe respective track runs occurs within that collinear alignment. Thethread orientation of tapered external helical threaded members 36 and40 are opposite of each other such that their rotation will result inopposite directional movement with respect to each other. Also, shaft 46passes through and engages tapered external helical threaded members 36and 40. However, the orientation of tapered external helical threadedmembers 36 and 40 is reversed from the orientation of tapered externalhelical threaded members 34 and 38. Under this orientation, as shaft 46is rotated by its end 50 in a counter-clockwise direction, taperedexternal helical threaded members 36 and 40 are rotated and theirrespective thread orientations cause the screws to travel apart fromeach other along track run 24 and track run 28, respectively.Correspondingly, as shaft 46 is rotated by its end 50 in a clockwisedirection, tapered external helical threaded members 36 and 40 arecaused to travel towards each other along track run 24 and track run 28,respectively.

As shown in FIG. 2, the step tracking is configured with a cascadingseries of risers of increasing height. For example, each track run hasrisers 52-60 as shown for step tracking 18 in FIG. 2. As the thread of atapered external helical threaded member travels into the gap betweenriser 52 and 54, the positional height of the tapered external helicalthreaded member body, as supported on risers 52 and 54, increases withinthe housing 12. As the tapered external helical threaded membercontinues to travel along the track run, its thread passes from the gapbetween risers 52 and 54 and enters the gap between risers 54 and 56which raises the tapered external helical threaded member body furtherwithin housing 12 as it is supported on risers 54 and 56. As the taperedexternal helical threaded member continues its travel along theremainder of the step risers 58 and 60 its positional height increasesfurther. As the positional height of the tapered external helicalthreaded member body increases, it urges top shell 14 apart from bottomshell 16 as shown in the series of FIGS. 7A-7C. The combined effect ofrotating the tapered external helical threaded members to cause theirmovement towards the outer ends of the respective track runs causes anexpansion of the housing 12 as shown in FIG. 7. The fully expanded shellis shown in FIG. 10. The housing 12 may be contracted by reversing themovement of the tapered external helical threaded members such that theytravel back along their respective track runs towards the midpoint ofthe housing. The housing will optimally provide expansion andcontraction to give the implant device a height over a range of aroundapproximately 7.8 mm to 16.15 mm in the present embodiment. The deviceof this embodiment of the invention can be adapted to provide differentexpansion dimensions.

The pairs of tapered external helical threaded members in each collineardual track run may be rotated independently of the pair of taperedexternal helical threaded members in the parallel track run. In thisarrangement, the degree of expansion of that portion of the housing overeach collinear track run may be varied to adjust the lordotic effect ofthe device. As an example shown in FIG. 8, tapered external helicalthreaded members 36 and 40 have been extended to a particular distancealong track run 24 and track run 28, respectively, causing the top shell14 to separate from bottom shell 16 thereby expanding housing 12.Tapered external helical threaded members 34 and 38 have been extendedto a lesser distance along parallel track run 22 and 26, respectively,causing that portion of the top shell over track runs 22 and 26 toseparate from bottom shell to a lesser degree. The series of FIGS.15A-15C show this effect where tapered external helical threaded members36 and 40 are extended apart from each other in further increasingincrements where the tapered external helical threaded members 34 and 38maintain the same relative distance to each other.

In FIG. 15A, the respective positioning of the set of tapered externalhelical threaded members 36-40 is approximately the same as the set oftapered external helical threaded members 34-38 in their respectivetracking. In this position, the top shell 14 is essentially parallelwith bottom shell 16. In FIG. 15B, the set of tapered external helicalthreaded members 36-40 move further distally apart along their trackingas the set of tapered external helical threaded members 34-38 remains attheir same position in FIG. 15A. In this setting, the lateral edge oftop shell 14 along which tapered external helical threaded members 36and 40 travel is moved higher with respect to the lateral edge of topshell 14 along which tapered external helical threaded members 34 and 38travel, giving a tilt to top shell 14 with respect to bottom shell 16.In FIG. 15C, the set of tapered external helical threaded members 36-40move even further distally apart along their tracking with respect tothat of the set of tapered external helical threaded members 34-38,giving an even greater tilt to top shell 14 with respect to bottom shell16. Through the independent movement of the respective tapered externalhelical threaded member sets, the device can achieve a lordotic effectof between 0° and 35° in the present embodiment. The device of thisembodiment of the invention can be adapted to provide different lordotictilt dimensions.

The tapered external helical threaded members have a configurationcomprising a body profile that has an increasing minor diameter fromD_(r1) to D_(r2) as shown in FIG. 5. The threads 33 have a pitch tomatch the spacing between the riser elements 52-60 in the tracking runsas shown in FIG. 4. Threads 33 can have a square profile to match theconfiguration between the risers, but other thread shapes can be used asappropriate. The increasing diameter and tapering aspect of the helicalthreaded members cause top shell 14 and bottom shell 16 to move apart asdescribed above. The contact at the tops of the risers 52-60 is made atthe minor diameter of the helical threaded member.

Thrust bearings are provided to limit the axial direction motion of thedrive shafts within shell 12. As shown in FIG. 9A, thrust bearing 62comprises a two-piece yoke configuration that mate together andpress-fit around ends of the shafts. The top part 64 of the thrustbearing yoke defines openings for receiving a round portion 66 of theshaft ends. In FIG. 9C, square shaft 42 has a rounded portion 66 oflesser diameter than the square portion of the shaft. A mating piece 65of the thrust bearing engages with top part 64 to encircle the roundedportion 66 of drive shaft 42. Pin elements 68 in the top portion 64 andbottom portion 65 engages corresponding holes 69 in the mating piece toprovide a press fit of the thrust bearing around the shaft. Journalgrooves 67 can also be provided in thrust bearing 62. Shaft 42 can havean annular ridge 63 around its rounded portion 66 which is received injournal groove 67 as shown in FIG. 9C. A thrust bearing is provided ateach end of the drive shafts as shown in FIG. 9B. As shown in FIG. 6,the thrust bearings restrict the axial movement of the drive shafts inthe housing.

A safety lock is provided at the proximal end of the device forpreventing unintended rotation of the shafts. As shown in FIGS. 12A and12B, safety lock member 70 is provided for engagement with the proximalends of drive shafts 42 and 46. The openings 73 in safety lock member 70are configured with the shape of the cross-sectional configuration ofthe drive shafts (see FIG. 13A). A portion of the drive shafts has anarrowed, rounded configuration 71 such that the drive shaft can rotatefreely while the rounded portion of the shaft is in alignment with thesafety lock member openings 73 (see FIG. 13C). FIG. 12B shows thisrelationship among the safety lock member 70, thrust bearing 62 anddrive shafts 42 and 46. When the non-narrowed portions 75 of the shaftsare placed in alignment with the safety lock member openings 73, thenrotation of the shafts is prevented (see FIG. 13B). FIG. 12A shows thisrelationship among the safety lock member 70, thrust bearing 62 anddrive shafts 42 and 46. A compression spring 77 can be placed betweenthrust bearing 62 and safety lock member 70 to urge safety lock memberback over the square portion 75 of the drive shafts. FIG. 12B shows alock disengagement when the safety lock member 70 is pushed forward outof alignment with the square portions 75 and placed in alignment withthe rounded portions 71 of shafts 42 and 46. Post 79 can be disposedbetween safety lock member 70 and thrust bearing 62 on which compressionspring 77 can be positioned. Post 79 can be fixedly connected to safetylock member 70 and an opening can be provided in thrust bearing 62through which post 79 can slide. Post 79 is provided with head 81 tolimit the backward movement of safety lock member 70 from thecompressive force of spring 77.

The interaction of the tapered external helical threaded members withthe step tracking contributes to self-locking under a power screwtheory. In considering the variables for promoting a self-locking aspectof the tapered threaded members, certain factors are relevant. Inparticular, those factors include the coefficient of friction of thematerials used, such as Ti-6Al-4V grade 5, the length of pitch of thehelical threads and the mean diameter of the tapered member. Thefollowing equation explains the relationship among these factors indetermining whether the tapered external helical threaded members canself-lock as it travels along the step tracking:

$T_{R} = {\frac{{Fd}_{m}}{2}\left( \frac{l + {\pi\;{fd}_{m}\sec\;\alpha}}{{\pi\; d_{m}} - {{fl}\;\sec\;\alpha}} \right)}$

The above equation determines the torque necessary to apply to the driveshafts engaging the tapered external helical threaded members forexpanding the shell members. This torque is dependent upon the meandiameter of the tapered external helical threaded members, the load (F)applied by the adjacent vertebral bodies, the coefficient of friction(f) of the working material, and the lead (1) or, in this embodiment,the pitch of the helical threading. All of these factors determine therequired operating torque to transform rotational motion into a linearlift to separate the shell members in accomplishing expansion andlordosis.

The following equation describes the relationship among the factorsrelating to the torque required to reverse the tapered external helicalthreaded members back down the tracking:

$T_{R} = {\frac{{Fd}_{m}}{2}\left( \frac{{\pi\;{fd}_{m}} - l}{{\pi\; d_{m}} + {fl}} \right)}$

Under this equation, the torque required to lower the tapered externalhelical threaded members (T_(L)) must be a positive value. When thevalue of (T_(L)) is zero or positive, self-locking of the taperedexternal helical threaded members within the step tracking is achieved.If the value of (T_(L)) falls to a negative value, the tapered externalhelical threaded members are no longer self-locking within the steptracking. The factors that can contribute to a failure to self-lockinclude the compressive load from the vertebral bodies, the pitch andmean diameter of the helical thread not being adequately great, and aninsufficient coefficient of friction of the material. The condition forself-locking is shown below:πfd _(m) >l

Under this condition, it is necessary to select an appropriatecombination of sufficient mean diameter size of the tapered member,along with the product material being a greater multiple than the leador pitch in this particular application so that the tapered members canbe self-locking within the step tracking. Based upon average values witha patient lying on their side, the lumbar vertebral body cross sectionalarea is around 2239 mm² and the axial compressive force at that area is86.35 N. With the working material selected to be Ti-6Al-4V, theoperating torque to expand shell housing 12 between L4-L5 of thevertebral column is around 1.312 lb-in (0.148 N-m), and the operatingtorque to contract shell housing 12 between L4-L5 of the vertebralcolumn is around 0.264 lb-in (0.029 N-m).

Alternate embodiments of the expandable shell housing provide fordifferent surgical approaches. FIG. 11A shows housing 100 for use wherea surgeon approaches the lumbar area from an anterior aspect of thepatient. The general configuration of the tracking runs for thisembodiment is similar to that for device 10, but the drive shafts formoving the tapered external helical threaded members are applied with atorque delivered from a perpendicular approach. For this, a dual set ofworm gears 102 and 104 respectively transfer torque to drive shafts 106and 108 as shown in FIG. 14.

FIG. 11B shows housing 200 for use where a surgeon approaches the lumbararea from a transforaminal aspect of the patient. The generalconfiguration of the tracking runs for this embodiment is also similarto that for device 10, but the torque is applied to the drive shaftsfrom an offset approach. For this, a dual set of bevel gears (not shown)may be used to transfer torque to drive shafts 206 and 208.

Housing 12 is provided with numerous niches and open areas in itssurface and interior regions to accommodate the storage of bone graftingmaterial. The interstitial spaces between the risers of the cascadingstep tracking also offers areas for receiving bone-grafting material. Amembrane can be provided as a supplement around housing 12 to helpmaintain compression on the top and bottom shells and to hold in bonegrafting material. Tension spring elements 78 can be provided to holdtogether top member 14 and bottom member 16 as shown in FIG. 10. Theseelements may also serve to provide an initial tension force in thedirection opposite of the expansion against the interbody fusion device.This allows the tapered external helical threaded members to climb therisers in the event that contact between the outer shells and thevertebral bodies is not yet made.

Accordingly, this embodiment of the interbody fusion device of theinstant invention is capable of expansion to provide support betweenvertebral bodies and accommodate the load placed on that region.Furthermore, the inventive interbody fusion device is capable ofachieving a configuration that can provide an appropriate lordotic tiltto the affected region. The device, therefore, provides a significantimprovement with regards to patient-specific disc height adjustment.

The device is provided with a tool for operating the interbody fusiondevice as it is adjusted in situ in a patient's spine. The operatingtool 300 is shown generally in FIG. 16 and comprises a handle member302, a gear housing 304 and torque rod members 306 and 308. The torquerod members connect to the drive shafts of expandable shell 12. Oneembodiment for connecting the torque rod members to the drive shafts ofexpandable shell 12 is shown in FIG. 17. In this arrangement, ends 48and 50 of drive shafts 42 and 46 can be provided with a hex-shaped head.The ends of torque rod members 306 and 308 can be provided withcorrespondingly shaped receivers for clamping around ends 48 and 50.

Within the gear housing 304, handle member 302 directly drives torquerod member 308. Torque rod member 308 is provided with spur gear member310 and torque rod member 306 is provided with spur gear member 312.Spur gear 312 is slidably received on torque rod member 306 and can movein and out of engagement with spur gear 310. Spur gear lever 314 engageswith spur gear 312 for moving spur gear 312 into and out of engagementwith spur gear 310. When torque rod member 308 is rotated by handle 302,and spur gear 312 is engaged with spur gear 310, rotation is translatedto torque rod member 306. In this condition, torque rod member 308rotates drive shaft 46 simultaneously with torque rod member 306 rotatesdrive shaft 42 to effect expansion of shell 12 as shown in FIGS. 7A-7C.Spur gear 312 can be moved out of engagement with spur gear 310 byretracting spur gear lever 314 as shown in FIG. 20. With spur gear 312out of engagement with spur gear 310, rotation of handle 302 only turnstorque rod member 310. In this condition, torque rod member 308 rotatesdrive shaft 46 solely and drive shaft 42 remains inactive to effect thetilt to the top member of shell 12 as shown in FIG. 8 and FIGS. 15A-15Cto achieve lordosis.

To achieve expansion of the device in the described embodiment, theoperator will turn handle member 302 clockwise to engage torquing. Thisapplied torque will then engage the compound reverted spur gear traincomposed of spur gear members 310 and 312. This series of gears willthen spin torque rod members 306 and 308 in opposite directions of eachother. Torque rod member 310 (in alignment with handle member 302) willspin clockwise (to the right) and torque rod member 306 will spincounterclockwise (to the left). The torque rod members will then rotatethe drive shafts of interbody fusion device 12 expanding it to thedesired height.

To achieve lordosis the operator will move the spur gear lever 314 backtowards handle member 302. By doing so spur gear 312 connected to torquerod member 306 is disengaged from the overall gear train, which in turnwill disengage torque rod member 306. As a result, torque rod member 308will be the only one engaged with the interbody fusion device 12. Thiswill allow the operator to contract the posterior side of the implantdevice to create the desired degree of lordosis.

Although the invention has been disclosed with reference to variousparticular embodiments, it is understood that equivalents may beemployed and substitutions made herein without departing from the scopeof the invention.

Having thus described the preferred embodiment of the invention, what isclaimed as new and desired to be protected by Letters Patent includesthe following:
 1. A spinal implant device for placement betweenvertebral bodies, the device comprising: a housing; at least one screwmember in the housing, the at least one screw member having athrough-opening; and at least one drive shaft in the housing extendingsubstantially from a first end to a second end of the housing, the atleast one drive shaft passing through the through-opening in the atleast one screw member; wherein the housing comprises a first shellmember and a second shell member, at least the first shell member havingat least one riser member for receiving the at least one screw member,the at least one drive shaft is operable to rotate the at least onescrew member, whereby the at least one screw member rotates with andtravels along the at least one drive shaft, the at least one screwmember is engageable with the at least one riser member, the at leastone screw member having a tapered configuration, whereby rotation of theat least one screw member increases a diameter of the at least one screwmember at a point of engagement with the at least one riser member,causing the first shell member and second shell member to move relativeto each other to effect expansion of the housing.
 2. The spinal implantdevice of claim 1, whereby the housing can be contracted by reversing adirection of rotation of the at least one screw member from that forexpansion, decreasing the diameter of the screw member at the point ofengagement with the at least one riser member.
 3. The spinal implantdevice of claim 1, wherein the at least one riser member comprises aseries of riser members of successively greater heights.
 4. The spinalimplant device of claim 3, whereby the at least one screw member isengageable with at least two successive riser members of the series ofriser members at a time.
 5. The spinal implant device of claim 4,whereby the series of riser members has gaps between individual risermembers of the series of riser members, whereby the at least one screwmember has a helical thread which can be received in the gaps.
 6. Thespinal implant device of claim 5, whereby rotation of the at least onescrew member causes the at least one screw member to travel along theseries of riser members, whereby rotation of the at least one screwmember increases the diameter of the at least one screw member at thepoint of engagement with the at least one riser member, causing at leastthe first shell member and the second shell member to move relative toeach other to effect expansion of the housing.
 7. The spinal implantdevice of claim 6, whereby the housing can be contracted by reversingthe direction of rotation of the at least one screw member from that forexpansion, decreasing the diameter of the at least one screw member atthe point of engagement with each successive riser member, and causingthe at least one screw member to travel in reverse on the series ofriser members of successively greater heights.
 8. The spinal implantdevice of claim 7, wherein the at least one riser member of the firstshell member comprises the series of riser members of successivelygreater heights and a second series of riser members of successivelygreater heights, whereby the at least one screw member comprises a firstscrew member and a second screw member, whereby the series of risermembers receives the first screw member and the second series of risermembers receives the second screw member.
 9. The spinal implant deviceof claim 8, wherein each of the first and second screw members have athrough opening configured to allow the at least one drive shaft to passthrough and operably engage with the first and second screw members,whereby the first and second screw members are disposed such that adirectional orientation of the helical thread of the first screw memberis opposite to a directional orientation of the helical thread of thesecond screw member, whereby the first and second screw members move inopposite directions relative to each other upon rotation of the at leastone drive shaft.
 10. The spinal implant device of claim 8, furthercomprising a thrust bearing member engageable with the first and seconddrive shafts to limit axial movement of the first and second driveshafts.
 11. The spinal implant device of claim 10, further comprising alocking member engageable with the first and second drive shafts toselectively prevent rotation of the first and second drive shafts. 12.The spinal implant device of claim 1, further comprising a thrustbearing member engageable with the at least one drive shaft to preventaxial movement of the at least on drive shaft.
 13. The spinal implantdevice of claim 12, further comprising a locking member engageable withthe at least one drive shaft to selectively prevent rotation of the atleast one drive shaft.
 14. A spinal implant device for placement betweenvertebral bodies, the device comprising: a housing; at least one screwmember in the housing; and at least one drive shaft; wherein the housingcomprises a first shell member and a second shell member, at least thefirst shell member having a plurality of riser members for receiving theat least one screw member, the at least one drive shaft is operable torotate the at least one screw member, the at least one screw member isengageable with the plurality of riser members, the at least one screwmember having a tapered configuration, whereby rotation of the at leastone screw member increases a diameter of the at least one screw memberat a point of engagement with the plurality of riser members, causingthe first shell member and second shell member to move relative to eachother to effect expansion of the housing, wherein the second shellmember having a plurality of riser members for receiving the at leastone screw member, the plurality of riser members of the first shellmember have gaps between riser members, the plurality of riser membersof the second shell member have gaps between riser members, wherein thegaps of the first shell member each have a position corresponding topositions of riser members of the second shell member and vice versa,thereby permitting the plurality of riser members of the first shellmember and the plurality of riser members of the second shell member tointermesh.
 15. The spinal implant device of claim 14, whereby the atleast one screw member is simultaneously engageable with at least twosuccessive riser members of the plurality of riser members on the firstshell member and at least two successive riser members of the pluralityof riser members on the second shell member, whereby rotation of the atleast one screw member causes the at least one screw member to travelsimultaneously along the plurality of riser members on the first shellmember and the plurality of riser members on the second shell member,where rotation of the at least one screw member increases the diameterof the at least one screw member at points of engagement with eachsuccessive riser member, causing the first shell member and the secondshell member to move relative to each other to effect expansion of thehousing.
 16. A spinal implant device for placement between vertebralbodies, the device comprising: a housing; a plurality of screw membersin the housing the plurality of screw members comprising at least onefirst screw member positioned along a first lateral area of the housing,and at least one second screw member positioned along a second lateralarea of the housing, the at least one first and second screw memberseach having a through-opening; a first drive shaft and a second driveshaft, the first and the second drive shafts extending substantiallyfrom a first end to a second end of the housing, the first drive shaftpassing through the through-opening in the at least one first screwmember, and the second drive shaft passing through the through-openingin the at least one second screw member; wherein the housing comprises afirst shell member and a second shell member, at least the first shellmember having at least one first riser member for receiving the at leastone first screw member, and having at least one second riser member forreceiving the at least one second screw member, the first drive shaft,positioned along the first lateral area of the housing, is operable torotate the at least one first screw member whereby the at least onefirst screw member rotates with and travels along the first drive shaft,the second drive shaft, positioned along the second lateral area of thehousing, is operable to rotate the at least one second screw memberwhereby the at least one second screw member rotates with and travelsalong the second drive shaft, the first drive shaft and second driveshaft being operable independently of each other, the at least one firstscrew member is engageable with the at least one first riser member, theat least one second screw member is engageable with the at least onesecond riser member, the plurality of screw members each having taperedconfigurations, whereby rotation of a screw member of the plurality ofscrew members increases a diameter of that screw member at a point ofengagement with a riser member of the at least one first riser member ora riser member of the at least one second riser member, causing thefirst shell member and second shell member to move relative to eachother to effect expansion of the housing, whereby contraction of thehousing can be effected from reversing a direction of rotation of thatscrew member from that for expansion, decreasing the diameter of thatscrew member at the point of engagement with the riser member, wherein adegree of expansion or contraction of the first lateral area of thehousing is independently adjustable relative to a degree of expansion orcontraction of the second lateral area of the housing when the at leastone first screw member and the at least one second screw member areindependently adjusted to different degrees of rotation.
 17. The spinalimplant device of claim 16, wherein the at least one first riser membercomprises a first series of riser members and the at least one secondriser member comprises a second series of riser members, each seriescomprising riser members of successively greater heights, each series ofriser members is for receiving one screw member of the plurality ofscrew members, whereby rotation of a screw member of the plurality ofscrew members causes that screw member to travel along a respective oneof the series of riser members of successively greater heights.
 18. Thespinal implant device of claim 17, whereby the at least one first screwmember comprises a first pair of screw members and the at least onesecond screw member comprises a second pair of screw members.
 19. Thespinal implant device of claim 18, wherein the first pair of screwmembers are disposed such that a directional orientation of the helicalthread of a first screw member of the first pair is opposite to adirectional orientation of a second screw member of the first pair,whereby the first and second screw members of the first pair move inopposite directions relative to each other along the first lateral areaof the housing upon rotation of the first drive shaft engaging the firstpair of screw members, wherein the second pair of screw members aredisposed such that a directional orientation of the helical thread of afirst screw member of the second pair is opposite to a directionalorientation of the helical thread of a second screw member of the secondpair, whereby the first and second screw members of the second pair movein an opposite direction relative to each other along the second lateralarea of the housing upon rotation of the second drive shaft engaging thesecond pair of screw members.
 20. The spinal implant device of claim 19,wherein the first and second pairs of screw members are disposed suchthat when the first drive shaft is rotated in a first direction thefirst pair of screw members move distally from the central portion ofthe first lateral area of the housing, and when the second drive shaftis rotated in a second direction opposite to the first direction thesecond pair of screw members move distally from the central portion ofthe second lateral area of the housing.
 21. The spinal implant device ofclaim 16, wherein the at least one first riser member of the first shellmember comprises a plurality of first riser members, the at least onesecond riser member of the first shell member comprises a plurality ofsecond riser members, and the second shell member comprises a pluralityof first riser members and a plurality of second riser members, theplurality of first riser members of the first shell member have gapsbetween riser members, the plurality of first riser members of thesecond shell member have gaps between riser members, wherein the gapsbetween the first riser members of the first shell member each have aposition corresponding to positions of the first riser members of thesecond shell member and vice versa, thereby permitting the plurality offirst riser members of the first shell member and the plurality of firstriser members of the second shell member to intermesh, and the pluralityof second riser members of the first shell member have gaps betweenriser members, the plurality of second riser members of the second shellmember have gaps between riser members, wherein the gaps between thesecond riser members of the first shell member each have a positioncorresponding to positions of the second riser members of the secondshell member and vice versa, thereby permitting the plurality of secondriser members of the first shell member and the plurality of secondriser members of the second shell member to intermesh.